It is known that correction of certain optical defects can be accomplished by imparting non-spherical corrective characteristics to one or more surfaces of a contact lens such as cylindrical, bifocal, or multifocal characteristics. However, the use of these lenses is problematic in that the lens must be maintained at a specific orientation while on the eye to be effective. When the lens is first placed on-eye, it must automatically position, or auto-position, itself and then maintain that position over time. However, once the lens is positioned, it tends to rotate on the eye due to blinking as well as eyelid and tear fluid movement.
Maintenance of the on-eye orientation of a lens typically is accomplished by altering the mechanical characteristics of the lens. For example, prism stabilization, including without limitation decentering of the lens' front surface relative to the back surface, thickening of the inferior lens periphery, forming depressions or elevations on the lens' surface, and truncating the lens edge, has been used.
Additionally, dynamic stabilization has been used in which the lens is stabilized by the use of thin zones, or areas in which the thickness of the lens' periphery is reduced. Typically, the thin zones are located at two symmetrically lying regions, one each on the superior and inferior regions of the lens periphery. A disadvantage of dynamic stabilization is that, when a dynamically stabilized lens is first placed on the eye, the lens may take between 10 and 20 minutes to auto-position itself. Thus, a needs exists for improved dynamic stabilization in which auto-positioning is achieved more quickly.